1. Field of the Invention
The invention relates to a rotary kiln and method of firing same for burning cement raw materials and the like.
2. Description of the Prior Art
The thermal energy necessary for the desired burning in a rotary kiln is usually procured by burning a fuel such as gas, oil or powder coal which is conveyed into a kiln through a burner.
The burner atomizes and distributes the fuel so as to bring it into close contact with an amount of air having sufficient oxygen content for nourishing the combustion so that combustion is carried out rapidly and efficiently in a controllable manner. A portion of the air necessary for supporting combustion is introduced through the burner under pressure. This portion of the air, known as the primary air, aids in the atomization and distribution of the fuel in the burning zone. Highly developed technology is necessary to construct a good burner for a rotary kiln for making cement, particularly since such a burner operates under severe conditions of heat and pressure. Such burners are exposed to constant heavy wear due to the large quantities of fuel that they convey and to an extensively dust-laden environment.
The rather complex construction incident to such a burner results in certain disadvantages. For example, functional defects arise easily and frequently result in impaired atomization and/or inadequate air mixing in the injected fuel. Further, the use of primary air, i.e. combustion supporting air fed directly to the burner gives rise to certain disadvantages. The primary air normally constitutes about 15 percent of the total amount of air fed to the burning zone. Unlike secondary air, i.e. air which is fed to the burning zone via alternate routes, other than the burner, the primary air is not preheated by the clinker charge. Accordingly, the increased utilization of primary air significantly decreases the heat economy of the kiln since primary air neither assists in recovering the heat contained in the clinker nor in transferring that heat to the burning zone of the kiln.
Norwegian patent specification No. 125,062 discloses a device for feeding liquid fuel directly into a rotary kiln through one or more tubes inserted radially through the side wall of the kiln. According to the Norwegian disclosure, a tube is provided at its outer end with a scoop device which scoops oil from a reservoir of fluid fuel during a portion of rotation of the rotary kiln and thereafter the oil flows through the tube into the interior of the kiln wherein it is gasified and ignited by the heat of the clinker.
The disclosure of the Norwegian patent does not, however, teach a method relating to the total firing of the kiln, but only to the introduction of oil and air into the kiln along the burning zone in order to prolong and regulate its temperature profile. However, the device according to the Norwegian patent utilizes the feature of locating the inlet device in the high temperature zone of the kiln. Moreover, although the tubes utilized possess greater strength and endurance than a conventional burner, they are nevertheless exposed to excessive wear and severe temperature impacts. Further, additional combustion air is introduced via tubes through the kiln wall thereby depriving the clinker cooler of a corresponding amount of cooling air.
I have invented a method of firing a rotary kiln and a rotary kiln which avoids the disadvantages of the prior art and is effective in improving the efficiency of the clinkering process.